1. Field of the Invention
This invention relates to the use of an amphoteric surfactant in combination with chlorhexidine and a non-ionic surfactant as the active antimicrobial agent in disinfecting and/or preserving solutions for contact lenses.
2. Description of the Prior Art
This invention relates to disinfecting and preserving contact lenses, particularly soft contact lenses. When the term "soft contact lenses" is used herein, it is generally referring to those contact lenses which readily flex under small amounts of force and return to their original shape when released from that force. Typically, soft contact lenses are formulated from poly(hydroxyethyl methacrylate) which has been, in the preferred formulations, crosslinked with ethylene glycol dimethacrylate. For convenience, this polymer is generally known as PHEMA. Soft contact lenses are also made from silicone polymers typically crosslinked with dimethyl polysiloxane. As is known in the art, conventional hard lenses, which cover only the cornea of the eye, usually consist of poly(methylmethacrylate) crosslinked with ethylene glycol dimethacrylate.
Hard contact lenses do not absorb appreciable amounts of water as do some soft contact lenses and thus the use of harsher disinfecting and cleaning agents does not create a problem in the hard contact lenses cleaning area. However, many hard lens disinfecting and preserving solutions contain benzalkonium chloride or chlorobutanol which may render the treated lenses hydrophobic, may not be stable in solution or lack compatibility with certain types of hard lenses, e.g., high silicone content. As is generally known, the users of soft contact lenses are warned against using solutions made for hard contact lenses since the materials in the solutions, as mentioned, may be absorbed or even concentrated by the soft contact lenses and may seriously damage the soft contact lenses or the eye of the user.
U.S. Pat. Reissue No. 29,693, R . E. Phares, Jr., discloses the use of chlorhexidine and its salts, such as chlorhexidine digluconate, as the active agent in soaking and sterilization solutions for soft contact lenses. Preferably the solution is isotonic.
U.S. Pat. No. 3,855,140, M. R. Billany et al, discloses cleaning compositions containing a soluble salt of chlorhexidine, a polyoxyethylene polyoxypropylene block copolymer and an inert diluent or carrier. The compositions are useful as a preoperative scrub in surgical practice.
U.S. Pat. No. 4,013,576, S. Loshaek, discloses an aqueous contact lens treating composition containing a bacteriocide and an amphoteric surfactant as a detergent. The solution provides cleaning, wetting, soaking and cushioning of the lens. Among the useful bacteriocides disclosed are thimerosal, biopal, chlorhexidine and benzalkonium chloride, however, no data is given for chlorhexidine. The amphoteric surfactant has the formula ##STR1##
The structure is illustrated in the ionized form as it exists in aqueous media. In this structure, R represents a hydrophobic group and consists of an acid radical such as the fatty acid radicals of C.sub.6 -C.sub.18 (coconut oil, lauric acid, capric acid, caprylic and ethylhexoic acid, oleic acid, linoleic acid and stearic acid); R.sub.2 is ##STR2## M and M.sub.1 are cation salt forming groups, such as hydrogen or alkali metals, X is OH, or the acid group of an anionic surface active agent, e.g., sodium lauryl sulfate or sodium lauryl sulfonate, R.sub.1 is H, or ##STR3## provided, however, when R.sub.1 is hydrogen M.sub.1 is absent, and n is an integer from 1 to 40. Materials of this type are offered commercially under the tradename "Miranol".
U.S. Pat. No. 4,046,706, J. Z. Krezanoski, discloses an aqueous contact lens cleaning composition comprising (a) a poly(oxyethylene) poly(oxypropylene) block copolymer having a molecular weight between 1900 and 15,500 and a cloud point above 30.degree. C., (b) ethyl or isopropyl alcohol and (c) an amphoteric surfactant having the formula ##STR4## in which R is a C.sub.6 to C.sub.24 hydrocarbon radical, selected from straight or branch chain, saturated or unsaturated, aliphatic hydrocarbon or an alkyl aryl group in which the alkyl group contains at least six carbon atoms, R.sub.1 is H, alkali metal, or CH.sub.2 COOM; R.sub.2 is a C.sub.1 to C.sub.4 alkylene group; Z is ##STR5## M is alkali metal, H or a nitrogen containing organic base; and G is OH, or a radical comprising the acid group of a C.sub.6 to C.sub.24 anionic surface active sulfate or sulfonate.
Also of interest is U.S. Pat. No. 4,199,567, B. F. Rankin, which discloses chlorhexidine gluconate containing solutions are stabilized against precipitation upon freezing by the addition thereto of certain nonionic surfactants.